Electromagnetically controlled solenoidal valves are commonly used to control the passage of gasses and liquids from a pressurized region into a chamber. Because of the large mechanical masses associated with the solenoid plunger related structures, these prior art devices are slow, often on the range of several milliseconds to open or close. Numerous emerging fields require an electrically controlled gas valve with faster response time.
In flash x-ray machines, a supersonic shell or cylinder of gas is compressed by high currents to form a dense, hot plasma pinch, which radiates the desired x-rays in a short pulse.
In laser-wakefield acceleration (LWFA) devices, it is possible to provide electron accelerators with unprecedented electric field gradients. In this application, supersonic and highly collimated gas jets and gas-filled capillary discharge waveguides are two primary targets of choice for LWFA. Present gas jets have lengths of only 2-4 mm at densities of 1-4×1019 cm−3, sufficient for self-trapping and electron acceleration to energies up to approximately 150 MeV. While 3 cm capillary structures have been used to accelerate beams up to 1 GeV, when using gas jets, a well collimated beam that is ≧10 mm in length, <500 μm in width and with the ability to tailor the gas density profile to optimize the LWFA process is required.
In other accelerators, it is sometimes desirable to inject a metered pulse of gas into a beam-line or test cell. One difficulty in the prior art is the requirement for precise control of the mass injected so that only the region of interest is filled with gas, while the rest of the accelerator structure can remain at high vacuum. For this application, the gas burst must be fast enough so that a high vacuum event may occur before the injected gas reaches the high vacuum region to perturb it.
To provide an example of the time scales involved, consider a typical supersonic gas velocity of 500 m/s. Gas will propagate a distance of 0.5 m in 1 millisecond. Hence, to ensure that the region beyond 0.5 m is unperturbed by the injected gas, the entire gas burst should be completed in less than 1 millisecond. A high-speed gas valve is desired where the valve opens in approximately 100 microseconds and is fully closed in approximately 500 microseconds.